The present invention relates to machine tools and milling machines and more particularly to automatic milling machines generally known as machining centers capable of multifunction CNC milling operations. More specifically, the invention concerns an improved chassis or base structure and associated carriages for the tool holder and workpiece holder support for sliding motion relative to each other.
During machining of a workpiece thrust forces amounting up to 1000 Kg may be present between the workpiece holder assembly on the one hand and the tool holder assembly on the other hand, acting in various directions according to the machining process. Accepted precision standards require that during the machining of a workpiece having a length of 300 mm, the deflection should not exceed 0.01 mm. It can thus be appreciated that the accuracy requirements of assemblies and of the mounting thereof are extremely high, bearing in mind that the deflection of a beam under bending moments is proportional to the third power of its length.
The achievement of such extreme accuracy and machining reliability under static as well as dynamic working conditions dictates a base structure of high rigidity and extremely heavy structure. As a typical example, a machining center capable of machining a workpiece measuring about 300 mm in each direction necessitates a base structure weighing no less than 2 to 3 tons and measuring a floor space of approximately 3 square meters.
Mainly because of these factors, machine tools of the kind referred to require highly sophisticated manufacturing techniques and know how, and are in fact manufactured only by a few enterprises in the world and are highly expensive.